The genes of all organisms are controlled so that they are only expressed in necessary amounts and at necessary times. The molecular level of this control usually takes place at sites on DNA which interact with control proteins. This project will determine the DNA sequence of the entire genetic control region (about 300 base pairs) of the histidine operon from Salmonella typhimurium. The objective is to understand the detailed molecular mechanism of genetic control for this operon. I ask such molecular quesions as: What sequences within the DNA control region are recognized as start signals and stop signals by RNA polymerase? What sequences are recognized by positive or negative genetic conrol proteins such as activators, repressors or termination factors? How do such control proteins activate or depress DNA star or stop signals as seen by RNA polymerase? Many of the available 100 regulatory mutants will be sequenced as an indispensable and invaluable aid to interpretation of the sequence. Bacterial genetic control mechanisms and their mutant variations could form a basis for understanding at the DNA level the possibilities for the stable genetic transformation of normal cells into cancerous cells that its the primary cause of cancer. Rapid DNA sequence determining techniques such as the recently devised primer-dependent technique of partial ribosubstitution will be employed as much as possible. The DNA primers will be restriction enzyme fragments. The DNA substrate will be a col E1 plasmid carrying the target histidine operon, constructed and modifed by the technique of in vitro genetic engineering. As far as possible, the genetic and sequencing technology developed and employed in this project will be those generally applicable to any DNA, including eukaryotic DNA, once it has been cloned on a plasmid.